The invention relates to a process for producing beers having yeast turbidity, in particular wheat beer, in which hopped beer wort is fermented by addition of yeast, after which the beer thus produced is packaged into suitable containers. Processes of this type have long been known for brewing white beer or wheat beer, Krausen beer and other beers having yeast turbidity and are very widely used. Since the previously prevailing close physical proximity of the breweries to their surrounding area due to the available storage and transport possibilities has been to a great extent abolished, beers of such types are now also stored for relatively long periods and some are even exported to distant foreign countries under severe climatic conditions.
The requirements thus newly created of keeping quality and sterility of the beers require corresponding measures, some of which conflict with the requirements regarding flavor stability.
The atmospheric oxygen conjointly introduced into the container during filling is a considerable problem. The beer present in the container reacts with this oxygen in the course of time, which leads to a decrease in flavor quality. In bottling, there has therefore been a changeover to evacuating the bottles, then flushing them with carbon dioxide, pressurizing them with carbon dioxide and then bottling the beer. The bottles are finally sealed gas-tightly with a crown cork. However, even in this process, a certain amount of atmospheric oxygen still enters the bottle during the bottling operation.
During canning of the beer, this problem becomes of still greater importance. Since the can, because of its inadequate pressure resistance, cannot be optimally evacuated during filling, and, in addition to this, offers a greater surface area, considerably more oxygen passes into the can than during bottling.
In brewing technology, in addition, the bottle fermentation process is widespread. In particular in the case of wheat beers, prior to packaging, the beer, which may have been heat-treated for a short time, is admixed with further beer wort and yeast. The added residual extract is then fermented in the bottle, as a result of which the oxygen in the container is consumed. However, in this secondary fermentation, which generally takes place over weeks, fermentation byproducts are also formed and the exhausted yeast remains in the beer, which can lead to a reduction in flavor quality.
For sale of beer to distant countries, it is moreover important that, after packaging, thermal destruction of microorganisms, e.g. by pasteurization, is performed in the packages, in order to ensure sterility and to prevent product damage, such as flavor impairment, by the action of beer-spoilage microorganisms. However, this approach has the considerable disadvantage that the yeast introduced for the purpose of secondary fermentation can no longer develop its activity and thus the oxygen in the container is no longer metabolized. In addition, the tendency of the oxygen to react with the beer present in the container is activated, or enlivened, at higher temperatures and, thus, by the temperature increase in the pasteurization, which leads to an accelerated "aging process" of the beer. Owing to the interaction with the oxygen, the flavor quality of the beer therefore deteriorates with time, which is further reinforced by temperature effects and movements.
Although the addition of active compounds, such as ascorbic acid or vitamin C, which is sometimes practiced in the case of other beverages can restrict these problems, in some countries it is not used for beer in view of a purity law, such as in Germany.